Coal is mined for use in the production of the energy that we use to power our homes and offices. These rocks may look like simple black, lumps, but they are unique in their content and ability to produce energy. Interestingly, there are four types of coal making it a diverse and fascinating rock.
How Coal Forms
Coal is a brownish-black colored rock that creates energy as it burns. Coal forms from dead plant matter that builds up in swampy, watery areas of our plant. As the shrubs and trees die in the swamp, they fall and stack up on top of each other. Over time, these dead plants, form layers and start to decompose, or rot, and break down and form a material called “peat.” The peat is buried deeper and deeper below the land surface as more layers of plant matter, rocks, and sediment deposit on top. As the layers become deeper underground, the pressure and heat rise, and change the peat into coal. Coalification is the name of the coal creation process.
Types of Coal and Their Ranking
There are 4 main types of coal. Coal varieties are both sedimentary rock and metamorphic rock. The three types of sedimentary coal are lignite, sub-bituminous, and bituminous. Anthracite is a variety of metamorphic coal. Experts rank coal by the amount of carbon inside the coal and the amount of heat that it can produce when it is burned.
The ranking order for coal is Lignite coal being the lowest rank, then Sub-Bituminous, Bituminous, and then Anthracite, which is the highest rank of coal and the most desirable variety for both energy companies and Santa!
Lignite Coal
Lignite coal has 25%–35% carbon and produces the lowest energy of all coal. It is the youngest coal and spends the least amount of time underground being exposed to high heat and pressure. It is one of the easier varieties to identify because it is very lightweight and looks very dull. Lignite Coal is also very crumbly and has a lot of moisture compared to other types.
Sub-Bituminous Coal
Sub-Bituminous Coal has 35%–45% carbon. It produces more energy than Lignite but less than Bituminous coal.
Bituminous Coal
Bituminous Coal is the most abundant type of coal in the United States. It has 45%–86% carbon. It is much harder than lignite coal, so it is not crumbly. But it still has a dull appearance.
Anthracite Coal
Anthracite Coal contains 86%–97% carbon and typically produces the most heat of all types of coal. One of the best ways to tell the difference in this type of coal is its luster. Anthracite tends to be shinier than all other types of coal. Interestingly, in the United States, northeastern Pennsylvania is the only location with anthracite. Other coal varieties are found in several states.
Coal is important to our way of life, but it is not a renewable resource. It takes millions of years for the coalification process to happen and create these different types of coal.
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